When working with a couple (or family, or individual) who has toxic arguments, it can be helpful to teach them about fair fighting rules. Be sure to practice in session, and come up with a specific plan for how a couple will implement the rules. Share a copy of this printout for your client to keep at home so they can be reminded of the rules when they need them the most. The first three rules include:
Before you begin, ask yourself why you feel upset. Are you truly angry because your partner left the mustard on the counter? Or are you upset because you feel like you're doing an uneven share of the housework, and this is just one more piece of evidence? Take time to think about your own feelings before starting an argument.
Discuss one issue at a time. "You shouldn't be spending so much money without talking to me" can quickly turn into "You don't care about our family". Now you need to resolve two problems instead of one. Plus, when an argument starts to get off topic, it can easily become about everything a person has ever done wrong. We've all done a lot wrong, so this can be especially cumbersome.
No degrading language. Discuss the issue, not the person. No put-downs, swearing, or name-calling. Degrading language is an attempt to express negative feelings while making sure your partner feels just as bad. This will just lead to more character attacks while the original issue is forgotten.